Skull Session
A million-year-old skull found in Ethiopia supports the theory that modern man evolved from a single pre-human species that developed in Africa and migrated throughout much of the world, scientists say.
Most anthropologists believe that Homo erectus — the species that is said to bear the first recognizable human characteristics — emerged nearly 2 million years ago in Africa and spread across several continents to serve as an ancestor to modern man, or Homo sapiens.
But some scientists maintain that another pre-human species known as Homo ergaster emerged in Africa about the same time, migrated around the world and evolved into Homo erectus. Then, according to this theory, Homo erectus traveled to Africa.
Tim White, an anthropologist at the University of California Berkeley who helped direct the study, said the skull settles for him the question of whether humans evolved from a single ancestor - Homo erectus.
"This new fossil is really important for two reasons," White said in a telephone interview.
"It sort of completes this series of fossils in Africa between 1.8 and half a million years ago that shows the lineage we call Homo erectus was an evolving lineage. This is a wonderful example of human evolution. You can see progressively human-like forms the younger you get in time."
The skull was found in a region of Ethiopia rich in the remains of early humans -- the Middle Awash area, about 140 miles northeast of Ethiopia's capitol Addis Ababa.
Henry Gilbert, working on his doctoral degree at Berkeley, found the skull in 1997. It took a year to completely remove the fossilized bone from the block of rock it was embedded in.
"When we cleaned the matrix off, we saw these weird scratches all across the top of the skull," White said.
A million years ago, large lions and huge hyenas lived in the area. "They would have had a gape big enough to crunch the entire face away in an attempt to get into the brain," White said.
The result was the skull has no face, but what is left of the cranium is enough for the experts to identify the species as Homo erectus, White said.
"This African fossil is so similar to its Asian contemporaries that it's clear Homo erectus was a truly successful, widespread species throughout the Old World," he said.
Many anthropologists have argued that fossils dating back as far as 1.7 million years actually belong to a separate species of humans, which they have dubbed Homo ergaster. The most recent example of Homo ergaster was found in the former Soviet republic of Georgia.
White argues that Homo ergaster is actually an early Homo erectus.
Homo erectus was actually a single, widespread species, White said. It did not start to fragment into different species, such as Europe's Neanderthals, until the Ice Ages separated populations.
Examples of Homo erectus include Java Man, found in what is now Indonesia, and Beijing Man, found in modern-day China.
These Asian branches never really evolved further and may have been replaced by modern Homo sapiens -- but White said there is not yet enough evidence to show what happened.
"When you stack these fossils up in time ... we see that somewhere between 100,000 and 200,000 years ago, anatomically modern people arose," White said.
These modern people then populated the world.
"They walked, but they didn't wake up one morning and say 'get out of here -- Pakistan looks better.' They said 'the hunting in the next valley is better'. It was like a diffusion or dispersion out of Africa," he said.